Cannot instantiate struct with field docstring interpolation

[aplavin]

MWE:

julia> "" struct S1
           " $(2*2) "
           x
       end

julia> S1(1)
ERROR: MethodError: no method matching S1(::Int64)

julia> methods(S1)
# 0 methods for type constructor:

help?> S1.x
  4

I would expect the result equivalent to the following:

julia> "" struct S
           " 4 "
           x
       end

julia> S(1)
S(1)

julia> methods(S)
# 1 method for type constructor:
[1] S(x) in Main at REPL[17]:2

help?> S.x
  4

I'm using the latest julia release:

julia> versioninfo()
Julia Version 1.6.2
Commit 1b93d53fc4 (2021-07-14 15:36 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Core(TM) i7-8565U CPU @ 1.80GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-11.0.1 (ORCJIT, skylake)